This invention relates to an improved process for the catalyzed conversion of oximes to amides which employs a HAMS-1B crystalline borosilicate-based catalyst composition. More particularly, this invention relates to the high conversion, high selectivity, and long catalyst life-time, gas phase catalyzed conversion of cyclohexanone oxime to caprolactam over a HAMS-1B crystalline borosilicate-based catalyst composition.
Caprolactam is a large volume commodity chemical used as a monomer in the production of the commercially important Nylon-6. Although routes to the precursor cyclohexanone oxime vary, all commercial caprolactam production makes use of a Beckmann rearrangement of the oxime. The commercial reaction is carried out in a batch operation in oleum (H.sub.2 SO.sub.4 .multidot.SO.sub.3) solution. The recovery step in this technology employs an ammonium hydroxide neutralization of the resulting caprolactam-oleum solution, a process generating two mols of by-product ammonium sulfate per mol of product. The sulfate has some value as a low grade fertilizer, but its disposal can add substantial cost to Nylon-6 production. Attempts have been made to circumvent the use of oleum and carry out the reaction in the gas phase; for example, BASF in a series of patents describes a supported catalyst containing boric acid (boric oxide) for the gas phase molecular rearrangement of cyclohexanone oxime to caprolactam in a fluidized bed. See e.g., Ger. Offen. Nos. 1,670,816, 2,059,703, and 2,641,429. Mobil, in Eur. Pat. Appl. No. 0056 698, teaches a gas phase process for the manufacture of the lactam by passing cyclohexanone oxime over a ZSM aluminosilicate molecular sieve catalyst having a SiO.sub.2 to Al.sub.2 O.sub.3 ratio of at least 12 and a Constraint Index of 1 to 12. Others have carried out the same reaction in the gas phase over polyphosphoric acid, U.S. Pat. No. 3,016,375, and over Zeolite Y. See J. Cat. 6, 247-53 (1966). Russian workers have used catalysts made from zeolites modified with amorphous aluminum borate or a mixture of aluminum oxide and boric oxide. See Dokl, Akad. Nauk., SSSR 26, 47 (1982) and Russian Inventor's Certif. Nos. 755,295 and 891,146. The last publication claims that the zeolite prepared by "simultaneous precipitation of aluminum and silicon hydroxide from aqueous solutions of their salts with subsequent modification with boric acid and addition of 30% decationized zeolite Y-type suspension" is a borosilicate. However, it is highly unlikely that the Russian material contains boron in the lattice and it is believed that none of the catalysts described combine high selectivity and catalyst lifetime with high conversion, a combination of prime importance for a commercial catalyst.
Now, it has been found that a catalyst composition comprising a supported HAMS-1B crystalline borosilicate sieve is capable of 100% conversion of cyclohexanone oxime to caprolactam at a selectivity to the caprolactam of over 80%. Additionally, the high conversion and selectivity can remain essentially constant over a very long catalyst composition lifetime.